CA1234584A

CA1234584A - Easy-working spray concrete

Info

Publication number: CA1234584A
Application number: CA000493712A
Authority: CA
Inventors: Kurt Allemann; Klaus Deneke; Hansjurgen Hass; Gunter Vogel
Original assignee: Dynamit Nobel AG
Current assignee: Evonik Operations GmbH
Priority date: 1984-10-27
Filing date: 1985-10-24
Publication date: 1988-03-29
Also published as: EP0191901B1; DE3569720D1; ES8704435A1; EP0191901A1; ES548224A0; PT81378B; PT81378A; US4772327A; KR860003177A; KR930009327B1; ATE42533T1

Abstract

ABSTRACT OF THE DISCLOSURE:

A readily processable spray concrete comprising concrete containing cement, a solidification accelerator in an amount of 2.0 to 5.0 weight-percent with respect to the cement content and a concrete liquefier, the solidification accelerator being a highly concentrated, aqueous-alkaline solution of potassium aluminate, potassium hydroxide and potassium carbonate having a molar ratio of K2O not bound as potassium carbonate to A12O3 between 1.1 and 1.6, a content in water of dilution such that the molar ratio H2O : A12O3 is between 9.5 and 30, and a potassium carbonate content of between 0.1 and 6 mol-%. And a method of preparing the spray concrete.

Description

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The present invention relates to a readily processable spray concrete and to a method of preparing it.
In particular, the present invention rela~es to a spray concrete that is easy to work even at a relatively low water-cement ratio, can be sprayed well, and sets and hardens rapidly. These properties are achieved by adding to the spray concrete certain concrete li~uefiers and accelerators before it emerges from the spray nozzle.
It is known to use as a starting mi~ture for the wet-spray process wet mixtures of cement, additives, water, and additives if used, as specified in DIN 18551. This wet mixture is delivered either pneumatically throllgh the spray nozzle to the point of application (thin-stream method) or it is pumped hydraulically to the spray nozzle (solid-stream method), where it is converted by compressed air to a thin ` stream. In both cases the wet mixture that is applied is in close contact with the water for a certain amount of time, which in practice can amount to as much as 90 minutes, and has already reacted with it.
It is also known to add an accelerator to a spray concrete so that thé concrete will set as rapidly as possible after it is sprayed on. The accelerator is added just before spraying, preferably directly as it is used at the point of application. The accelerators include concentrated solutions of alkali aluminates, alkali hydroxides and alkali carbonates, such as those described, for example, in U.S. patent 45 04 315. The accelerators cited therein exercise their full action in the dry spraying process when they are added together with the water (hereinafter also called "mixing water") to the dry-spray concrete according to DI~I~ 18551. Then they act spontaneously on the cement to accelerate setting in the mixing water at~the ~spray nozzle directly at the point of : ,~
, ~23~S~34 application of the spray concrete. If, however, the spray concrete has already been mixed with the mixing water for a longer period of time and has already reacted, as is the case in the wet-spray process, the accelerators described in U.S. patent 45 04 315 could no longer produce their optimum effect.
The sole use of liquid accelerators in the wet spray process can cause the consistency of the spray concrete after emerging from the nozzle to be too low, so that the concrete adheres insufficiently especially to vertical walls and overhead areas. Increasing the consistency of the spray concrete by adding lesser amounts of mixing water to obviate this disadvantage is impossible, because then the concrete will no longer be able to be pumped or driven, so that another way of avoiding this disadvantage must be sought.
One known answer to the problem of pumping spray concrete with a low water-cement ratio consists in adding known concrete liquefiers to the concrete. Such additives do increase the readiness of fresh concrete to be pumped and worked, yet they diminish the action of many commonly used accelerators. Thus for example, the solidification ; accelerating action of the potassium aluminate-base solidi-fication accelerators listed in U.S. patent 45 04 315 is partially or entirely cancelled by the known concrete liquefiers of technical grade based on alkalinized or neutralized salts of lignin sulfonates. This disadvantage is obviated by using known concrete liquafiers in conjunction with water glass. The latter, however, must be added in amounts between 10 and I5~ with respect to the cement in order to achieve an adequate hardening action.
These amounts, however, have the disadvantage, in turn, that the strength of the set concrete is diminished. The loss of

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strength can amount -to as much as 50~ and more.
The problem therefore was to find a spray concrete liquefying and strengthening system that would keep the spray concrete easy to work at the lowest possible water-cement ratios, so that it could easily be pumped in thespray equipment, and at the same time produce the quickest possible stiffening, setting and hardening of the concrete after leaving the spray nozzle. The liquefier contained in the system must the~efore not have a negative influence on the action OL the accelerator.
According to the present invention, there is ; provided a readily processable spray concrete comprising:
concrete containing cement, a solidification accelerator in an amount of 2.0 to 5.0 weight-percent with respect to the cement content, and a concrete liquefier, said solidification accelerator being a highly concentrated, aqueous-alkaline solution of potassium aluminate, potassium hydroxide and potassium carbonate having a molar ratio of K2O not bound as potassium car~onate to A12O3 between 1.1 and 1.6, a content in water of dilution such that the molar ratio H2O : A12O3 is between 9.5 and 30, and a potassium carbonate content of between 0.1 and 7 mol-%.
Such a spray concrete is especially readily workable and can easily be pumped in the known concrete spray e~uipment, adheres well to vertical walls and overhead surfaces without running down or falling off, and rapidly hardens to a solid mass of high end strength. Ready workability in the sense of the invention means that, for pumping and application, the concrete has a spread, which is correlated with its consistency, of at least 45 cm, i.e., it is adapted to the known given working conditions, without the occurrence of difficulties based on its composition.
The action of the above-named additives can be -~3 -~ ~ . ~
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further improved if the spray concrete additlonally contains silicate systems such as finely distributed or highly dispersed SiO2 or water-soluble alkali silicates in arnounts up to 3.0 weight-percent. Preferably the amount of these alkali silicates is between 0.25 and 2.0 weight-percent.
SiO2 can, preferably, be used in amounts up to 2.5%
depending on the SiO2 content or dispersity. Such a spray concrete with these additional components can also be used at tempertures below ~15 C. This is not possible in the case of the known spray-concrete mixtures which contain water glass in amounts of about 10.0 to 12.0 weight-percent, since the high viscosity of the wa-ter glass at these temperatures, if large amounts are used, has an unfavorable action.
On the basis of the above-named additions, the wet spray concrete according to the invention can have a water-cement ratio of about 0.44 to 0.55; preferably it is between 0.45 and 0.47 Preferably, the concrete liquefiers is one or more compounds from the class of naphthalinesulfonicacid-formaldehyde condensates. These products are substances which are used as dispersants for pigments and tanning agents. They are prepared by condensing the corresponding naphthalinesulfonic acids with formaldehyde and, if necessary, neutralized with lyes in aqueous solutlons. They are also referred to as condensation products of naphthalinesulfonic acid with formaldehyde (cf. Ullmann "Encyclopadie der techn. Chemie," 3rd ed~, vol. 17, page 80). Their use as concrete liquefiers is described, for example, in U~S~ PS 42 ~7 334. There, however, these substances serve only for the liquefaction of the system, and are not used in combination with solidification accelerators.

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In contrast to other concrete liquefiers, e.g., those on the basis of lignin sulfonates, they do not interfere with the action of accelerators according to the teaching of U.S. patent 45 04 315. Instead, they form with these accelerators a synergistic system which produces extraordinarily short setting times and a very good development of strength in spray concrete.
Preferably, the amount of concxete liquefier to be added is between 0.2 and 3.0 weight-percent with respect to the cement content of the spray concrete.
The amounts of the concrete liquefier to be used in practice will depend, for one thing, on the water-cement ratio of the wet mixture, on its composition, and on the compounds that are used. The optimum amount must therefore be determined by preliminary testing.
According to the invention, the solidification or setting acceleration are not added to the mixing water as described in U.S. patent 45 04 315, but to the wet mixture.
The optimum action of the spray concrete according 2~ to the present invention will depend on, among other things, the nature and amount of the concrete liquefier and on the rheological properties of the wet mixture in question.
According to the present invention, there is also provided a method of preparing a spray concrete comprising concrete containing cement, a solidification accelerator and a concrete liquifier,comprising injecting or blowing the liquefier and accelerator into a pumping and spraying system of a concrete spraying apparatus provided at the point of use of the spray concrete, wherein the concrete liquefier is put into the apparatus ahead of the pumping conduit and the setting accelerator after the end of the pumping conduit ahead of or within the spray nozzle.
According to the present invention there is also ., , , ~3~5~34 provided a me-thod of rendering a spray concrete easily workable and subsequently ~uick hardeni~g comprising injecting of blowing the liquefier and accelerator into a pumping and spraying system of a concrete spraying apparatus provided at the point of use of the spray concrete, wherein the concrete liquefier is put into the apparatus ahead of the pumping conduit and the setting accelerator after the end of the pumping conduit ahead of or within the spray nozzle, where said concrete has a cement content, at least one setting accelerator selected from the group consisting of alkaline aqueous solutions of potassium aluminate, potash lye and potassium carbonate, having a molar ratio of X20 not bound as potassium carbonate to Al203 between 1.1 and 1.6, a content in water of dilution such that the molar ratio H20 : Al203 is between 9.5 and 30, and a potassium carbonate content of between 0.1 and 6 mol-%.
The additives according to the invention are added to the fresh concrete preferably directly at the worksite.
They are preferably a1ded directly before spraying, /

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' means of known and appropriate feed means. The concrete liquefiers are incorporated insofar as possible immediately before the fresh concrete is introduced into the solid stream pumping system, while the concrete accelerator is added only at the end of the solid-stream pumping system, preferably ahead of or within the spray nozzle.
The water-soluble alkali silicates are sodium and potassium silicates, known in themselves, which are also known as soda or potash water glasses. The addition of these products can be performed either together with the concrete liquefiers or before or after the additlon of the hardening accelerators. The first-named variant makes possible the uniform distribution of these substances in a simple manner. If the concrete liquefier and alkali sili-cate are added simultaneously, however, the synergisticaction with the hardening accelerator is lower than when the silicates are added to the thin stream. In the case of addition to the thin stream, the alkali silicate develops its maximum effect. At the same time, however, it must be assured that the relatively small amount is accurate-ly proportioned and is well distributed in the thin stream.
In place of alkali silicates, the above-named highly dis-persed silicic acid (SiO2) can be used.
The admixture of the components according to the ~5 invention to the thin stream is performed by measures known in themselves, such as injection or spraying through a nozzle, using known devices.

Examples Fresh mortar was prepared from three parts standard sand according to DIN 1164, Part 7, and one part commercial Portland cement PZ-35F with a~ water-cement ratio of 0.52.
All components were at room temperature (about 21~C) or , .

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were cooled to about 10C. At these temperatures the fresh mortars were let stand for 30 minutes in each case. Then the additives listed in Table 1 and Table 2 were added at the end of the periods specified therein, in the same test amounts in each case.
The testing of the setting process was performed by means of a cone according to DIN 1168 with a test load of 270 gm, the diminishing depth of penetration being recorded at intervals of one minute. This depth of penetration, which is a measure of the setting speed, is specified in Table 1 as the "cone penetration depth." In Table 1, furthermore, A represents a concrete liquefier on the basis of naphthalinesulfonic acid-formaldehyde condensate in the form of a 40% solution. Proportion: 0.5 wt.-% with respect to the cement;
B represents alkali silicate solution in the form of a 35~ solution, used in the amount of 1.0 weight-percent with respect to the cement content, and C represents a concrete accelerator composed of potassium aluminate, potassium hydroxide and calcium carbonate according to the teaching of U.S. patent 45 04 315, in an approximately 50%
solution, in a proportion of 3.0 weight-percent with respect to the cement.

In the last column of Table 1 are listed the spread dimensions al5 of fresh concrete. 0 concretes (examples 1 and 4) are compared with fresh concretes to which the additives A and B according to the invention were admixed individually and in combination 30 minutes - after the fresh concretes were prepared. The measurements took place at the temperatures specified in Table 1. The _ 7 _ ..
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greater spread dimensions are an indication of the easier workability of the fresh concretes.
The composition of the test concretes was in accordance with the "Additive Guidelines." , according to german " Richtlinien fur die Zuteilung von Prufzeichen fur Beton-Ausatzmittel (Prufrichtlinien) Fassmug, February 1984" .
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~3~5~ 1 Examples 1, 4 and ~ are given for COmE~risOS~ , and do not ~ n~ol~e a compo~fition accordiny to the inventi~n as an additive. In thes~ examples either the ~pread a15 i~ too small, ~r also ~he settin~ is unfsati~a~tory. Although Example 7 fshows yood settlnq, ~ spread at 5 of 42 . 8 c~ does not ~ati~y the requirementff3 to l:e m~3t by the rhefological ~ehavior of a corre~pc,nding f~esh concrete upon dell~tery to the ~olid r,tream pumpinq system: as ~ ~ule, ~ spread a1 S
at least 45 cm is required. Wet mixtures havin~a a lasser spread al 5 must nc)t be used ln a ~olld st~eam pumping sy stem. f 'rhe requirem~nt for ~ sufficient ~pread ~5 o~ at lea~t 45 cm i~ ~tisf ied by th~ mixt~res of examples 2, 3, 5, ~ ~nd 8. Example~ 3 and ~ are very gc,od example6 of the s~nergis-tic action of additives A ~d B, e~pe~lally w~th ragard to ~tif~ening aCtic:~n.

A~ already ~t~ted above, the proportioning of B into C in the thin stream produces ~y f~r the strongest effe~t~ On ac~o~nt of the ex~remely short setting time it is dif f lc~lt to produce ~ relevant test ffspeclmen by ~he test method , , ' ~

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selected. The technical use of this proportioning variant thus places great demands on the system for proportioning B
in the thin-stream phase in spraying concrete. It must also be assured in this case that the barely still plastic spray material is sufficiently compressed upon application and that the splash-back remains within acceptable limits.
In a further comparative testing of the additive according to the invention, corresponding to the Examples 4 to 6 of Table 1, the setting performance E of the test mortar was measured with the Vicat* needle (DIM 1164, Part b). The wet mortars were prepared, unlike those of Table 1, with a water-cement ratio of 0.50 in accordance with DIN
1164, Part 7. The test temperature was 20 C, as in Examples 4 to 7 of Table 1. EB indicates the onset of hardening and EE the termination of hardening.

-* Vicat is a kind of a needle used in the concrete and cement industries.

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Table 2 o. T~ ~ Addltion of the addit~veaf~er 30 ' ~fter 45 ~
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4a 20 - C 1 '3û" 4'30"
5a 20 A C 1'15". 3'30"
6a 20 A~3 C 1'15" 3'15"

After the same tes~ proeedure, Example P~ o~ Table 1 ~aY also varie~ by using amoun~s o~ 0.25, 0,5, 1.0 ~nd 1.59~, w~ 1~
respect to the P~rtland cement, o~ th~ alkal~ poly~ilicate additive B. It wa~ then found that the pre~Jlo~A ly described spon~aneQus action of the additive ~c~m~ination wa~ produced by a proportion of nnly 0.25~6. The effeot wa~ observed even in the rnixing phase of the preparation ~f the s~mples within 2() t~- 4C~ se~onds after the ~ddi~ ic~n ~f C.

It will be unders~ood that th~ ~pe~ification and example~
are illustr~tiv~: but not limitat~ve of the pre~en~ invention and th~t oth~r em~ diments within the ~pirit and so ;7pe of the inventinn will ~ug~est themselves to those ~7cilled in the Art~ :

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A readily processable spray concrete comprising: concrete containing cement, a solidification accelerator in an amount of 2.0 to 5.0 weight-percent with respect to the cement content, and a concrete liquefier, said solidification accelerator being a highly concentrated, aqueous-alkaline solution of potassium aluminate, potassium hydroxide and potassium carbonate having a molar ratio of K2O not bound as potassium carbonate to A12O3 between 1.1 and 1.6, a content in water of dilution such that the molar ratio H2O : A12O3 is between 9.5 and 30, and a potassium carbonate content of between 0.1 and 6 mol-%.

2. The spray concrete of claim 1, wherein the molar ratio of K2O not bound as potassium carbonate to A12O3 is 1.15 to 1.45, the water of dilution has the molar ratio H2O : A12O3, between 11 and 25 and the K2CO3 content is 0.1 to 5 mol-%.

3. The spray concrete of claim 1 having a water-cement ratio between 0.44 and 0.55.

4. The spray concrete of claim 1 additionally containing up to 3.0 weight-percent of alkali silicates or highly dispersed SiO2.

5. The spray concrete of claim 1, wherein the concrete liquefier is of one or more compounds from the class of naphthalinesulfonicacid-formaldehyde condensates.

6. The spray concrete of claim 1 containing the concrete liquefier in an amount of 0.2 to 3.0 weight-percent with respect to the cement content.

7. A method of preparing a spray concrete comprising concrete containing cement, a solidification accelerator and a concrete liquifier,comprising injecting or blowing the liquefier and accelerator into a pumping and spraying system of a concrete spraying apparatus provided at the point of use of the spray concrete, wherein the concrete liquefier is put into the apparatus ahead of the pumping conduit and the setting accelerator after the end of the pumping conduit ahead of or within the spray nozzle.

8. A method of rendering a spray concrete easily workable and subsequently quick hardening comprising injecting or blowing the liquefier and accelerator into a pumping and spraying system of a concrete spraying apparatus provided at the point of use of the spray concrete, wherein the concrete liquefier is put into the apparatus ahead of the pumping conduit and the setting accelerator after the end of the pumping conduit ahead of or within the spray nozzle, where said concrete has a cement content, at least one setting accelerator selected from the group consisting of alkaline aqueous solutions of potassium aluminate, potash lye and potassium carbonate, having a molar ratio of K2O not bound as potassium carbonate to A12O3 between 1.1 and 1.6, a content in water of dilution such that the molar ratio H2O : A12O3 is between 9.5 and 30, and a potassium carbonate content of between 0.1 and 6 mol-%.

9. The method of claim 8, wherein the molar ratio of K2O not bound as potassium carbonate to A12O3 is 1.15 to 1.45, the water of dilution has the molar ratio H2O : A12O3 between 11 and 25, and the K2CO3 content is 0.1 to 5 %.

10. The method of claim 8, wherein the spray concrete contains the concrete liquefier in an amount of 0.2 to 3.0 weight-percent with respect to the cement content.

11. The method of claim 8, wherein the spray concrete contains the setting accelerator in an amount of 2.0 to 5.0 weight-percent with respect to the cement content.

12. The method of claim 8, wherein the spray concrete has a water-cement ratio between 0.44 and 0.55.

13. The method of claim 8, wherein the spray concrete additionally contains up to 3.0 weight-percent of alkali silicates or highly dispersed SiO2.

14. The method of claim 8, wherein the concrete liquelier is one or more compounds from the class of naphthalinesulfonicacid-formaldehyde condensates.